This invention relates to the electronic system for a release mechanism for an off-bottom seismometer, and more particularly to a system which reliably releases the seismometer unit in the event of power supply or other equipment failure.
On-bottom seismometers are deployed on the ocean floor to measure seismic energy, for example, that are repetitively produced by a seismic exploration vessel.
Recently, "pop-up" type on-bottom seismometers (OBS) have been increasingly used for deep water seismic exploration. Pop-up seismometers generally comprise a frame fitted with floats, instruments, power sources and ballast. Released at the ocean's surface, they are allowed to free fall to the ocean floor. Recovery is accomplished by the planned release of a ballast which allows the then buoyant assembly to float to the water's surface where it may be retrieved.
In recent years, a variety of ocean bottom seismometers have been constructed and used, each with its own release mechanism. In an article "Ocean Bottom Refraction Seismograph (OBRS)" published in Marine Geophysical Researches 3 (1978), F. Avedik, et al schematized an OBS release mechanism.
An electroplating stainless steel wire release mechanism was described by A. K. Ibrahim, et al at the 46th Annual Society of Exploration Geophysicists meeting of Oct. 24, 1976 in Houston Tex. The OBS in which the release mechanism was employed was relatively small (weighing approximately 170 pounds) and consisted of a single buoyant glass sphere mounted to a frame by three elastic straps joined together by a piece of stainless steel wire. Release was achieved by passing an electric current through the stainless steel wire causing it to electroplate into solution when exposed to sea water.
Many of the release mechanisms employed thus far have used explosive bolts as a means of releasing the ballast. Although relatively safe, explosive bolts represent a danger to personnel working with the OBS prior to its launch as well as during and after its recovery if an unexploded bolt is still present. Although redundant means of releasing the buoyant package have been utilized on OBS's, such systems generally employ more than one explosive bolt.